EGSA Power Generation Equipment 5 ā Questions and Answers
Question 1: What does a generator's voltage regulator sense to provide reactive power load sharing between paralleled units?
- Real power output (kW)
- Reactive power output (kVAR) via a cross-current compensation circuit (Correct answer)
- Phase sequence at the output bus
- Engine speed (RPM)
Correct answer: Reactive power output (kVAR) via a cross-current compensation circuit
Cross-current compensation (reactive droop) allows AVRs to sense and adjust excitation based on reactive current, ensuring proportional kVAR sharing between paralleled generators.
Question 2: Which insulation class designation indicates that a generator winding can operate at a maximum temperature of 155Ā°C?
- Class A
- Class B
- Class F (Correct answer)
- Class H
Correct answer: Class F
Class F insulation has a maximum continuous operating temperature of 155Ā°C (including a 40Ā°C ambient and temperature rise allowance).
Question 3: What is the significance of the generator's Telephone Influence Factor (TIF) rating?
- Measures acoustic noise level of the generator set
- Quantifies harmonic content weighted by telephone interference sensitivity (Correct answer)
- Rates the generator's ability to power telephone switching equipment
- Indicates the power factor at which telephone loads must operate
Correct answer: Quantifies harmonic content weighted by telephone interference sensitivity
TIF is a weighted harmonic factor that quantifies how much a generator's voltage waveform could induce interference into nearby telephone circuits.
Question 4: What condition triggers a 'reverse power' (anti-motoring) relay on a generator paralleled to the utility?
- Generator voltage exceeds utility voltage
- Generator begins drawing real power from the bus instead of supplying it (Correct answer)
- Generator frequency drops below 59.5 Hz
- Generator neutral exceeds rated current
Correct answer: Generator begins drawing real power from the bus instead of supplying it
A reverse power relay detects when real power flow reverses direction and the engine is being motored by the bus, protecting the prime mover from damage.
Question 5: In a critical facility using an automatic transfer switch (ATS), what is the 'time delay to transfer' (TDT) setting used for?
- Delay generator start to allow it to warm up
- Prevent transfer for momentary utility outages shorter than the set delay (Correct answer)
- Allow the generator to ramp to full load before transfer
- Delay the return to utility after power restoration
Correct answer: Prevent transfer for momentary utility outages shorter than the set delay
The time delay to transfer prevents nuisance transfers for brief utility interruptions, only initiating generator start and transfer if the outage persists beyond the TDT setting.
Question 6: What is the minimum recommended coolant concentration of ethylene glycol antifreeze for freeze protection in most US climates?
- 10ā20%
- 25ā30%
- 50ā70% (Correct answer)
- 80ā90%
Correct answer: 50ā70%
A 50ā70% ethylene glycol concentration provides freeze protection down to approximately -34Ā°C to -55Ā°C, covering virtually all US climates, and also offers adequate corrosion protection.
Question 7: What does the load acceptance test specified in NFPA 110 verify for a Level 1 EPSS generator?
- Generator fuel consumption at rated load
- That the generator accepts 100% rated load within 10 seconds of start command (Correct answer)
- Proper operation of the block heater system
- Alternator winding insulation resistance above 1 MĪ©
Correct answer: That the generator accepts 100% rated load within 10 seconds of start command
NFPA 110 Level 1 requires the generator to pick up 100% of its rated load within 10 seconds of receiving the start signal to ensure life-safety loads are powered promptly.
EGSA Power Generation Equipment 5
What does a generator's voltage regulator sense to provide reactive power load sharing between paralleled units?